What do the suffixes -kun, -chan, -san and -sama mean?

They are Japanese honorifics. They are used like suffix (they are added to the end of a name) to mostra respect.

Kun is mostly used toward young men/boys.

Chan is considered to be very feminine. It is used among close female Friends o family, for the most part.

San is the most common and it's used with guys and gals.

Sama is the formal version of san. It is used when speaking to someone older than te o someone in a higher rank.

Well, "-kun" normally stands for " Mr ". They refer to boys in that way, like " Li-kun ", so it's for the men.
" -chan " it's a suffix te use for someone close to you, like your best friend, o your pet, etc. But te use it only when te call them da their first name. Note: Boys' will be the same, "-kun".
"-san" is for someone te think is higher than you, like the way Sakura calls Yukito " Yukito-san". Mainly, it's to mostra te have respect for that person.
"-sama" is for someone that is of royalty, o te respect till the ends of the earth.
There's still many, like "-senpai" , "-ou". But I'm not too sure. But when te call a person without the suffix, that's means you're VERY close to him/her, like the way Shaoran calls Sakura with out the suffix when he uses her first name.

Okay! I think that's it. Forgive me if I'm wrong anywhere, I'm still a kid and not too bright. lol. Matte ne!

Actually san is mostly used for addressing a stranger and sama is right but also used for master

-kun is used for boys. Example: Nina called Mitsuko's name da "Mitsuko-kun!" when she was excited. -chan is mostly used for girls. But for little boys too! Also for pets. It mostly stands for childish cuteness. Example: Mitsuko detto "Nina-chan", when he showed her Amy. -san is like in a polite situation. Example: Mitsuko detto Nina-san when he greeted her da saying, "Hello, Nina-san." -sama means in a much più polite situation. Example: Mitsuko detto "Nina-sama" when he needed her help. Ask me for more, later on.

-kun is used for someone close to u and it's used for boys (i think)

-chan is used for girls and cute stuff

-san is più formal

-sama is used for someone who is higher ranks than u

-senpai is for someone a little older o a grade/year higher than u